488 THE FRESH-WATER LOCHS OF SCOTLAND 
AuscoT^ NAN. — Rock-basin in Lewisian Gneiss. 
AvicH. — Rock-basin in qiiartzites, phyllites, limestones, and epidiorites 
(Loch Awe group). Like Loch Awe^ the upper end of this loch is 
in part surrounded by a high terrace of sand and silt 200 feet above 
the present surface of the lake^ which must have been formed when 
the rest of the rock-basin was occupied by a lobe of ice projecting 
from the Loch Awe glacier. The height of this terrace was 
determined by the level of the col at the head of the valley over 
which the loch must have drained westwards into the Barbreck river 
towards Loch Craignish. 
Awe (Etive basin). — Valley rock-basin^ mostly along the strike of 
crystalline schists^ composed of altered sedimentary and igneous 
rocks (Loch Awe group)^ and partly along the shatter-belt of the 
Pass of Brander faulty in consequence of which the loch forks. The 
lake has two basins. The more southerly and longer one from Ford 
to the island of Inistrynich follows the strike of the strata, while the 
other coincides for some distance with the Pass of Brander shatter- 
belt and then bends nearly at a right angle towards the mouth of 
the river Orchy. The two basins are separated from each other by 
a comparatively shallow plateau, on which the rocky islands are 
situated. The study of the glaciation of the region shows that, 
during the confluent glacier period, the Pass of Brander, although 
of pre-glacial origin, was not sufficiently wide to drain off all the ice 
poured into the head of Loch Awe by the convergent glens of the 
Shira, the Orchy, and the Lochy. From the soundings of the Lake 
Survey it may be inferred that the ice that passed through the Pass 
of Brander worked along the comparatively weak belt of shattered 
rock in the pass, thus producing the peculiar L-shaped basin shown 
in the charts. The surplus ice streamed across the shallow plateau, 
and, gaining accessions from the Ben Lui and Ben Buidhe mountain 
masses, moved towards the south-west end of the lake. As the 
valley narrowed, the abrading action of the ice was increased, which 
resulted in the longer and deeper basin along the strike of the 
strata. The phenomena at the south-west end of the loch show 
that, at a period during the retreat of this confluent glacier, the 
Craig an Tairbh pass was choked by the ice, and the melt-water 
of the glacier escaped across a high col into the river Add above 
Kirkmichael Glassary. Thereafter it streamed through an inter- 
mediate gap into the Add by the lower end of the Kilmartin valley ; 
and subsequently, when the ice had farther retreated, by the Craig 
an Tairbh pass itself into the same valley above Kilmartin. During 
the recession a lobe of ice became detached and occupied the site 
of Loch Ederline, and was there surrounded by the fluvio-glacial 
travels from the melt-water of the glacier. A still farther retreat 
of the glacier left a lake occupying the south-west part of the 
existing Loch Awe, the level of which was determined by the 
